Tokeino Hari Manga

After their parents are killed in a plane crash, Ryuuichi and his younger brother Kotarou are taken in by the chairman, who they never met before, of an elite academy. Ryuuichi becomes the school daycare's new babysitter.

From Esthtique:Sakura had lived with her grandma ever since her parents died in a car accident when she was three. When she turned fourteen, her grandma also passed away, leaving her alone. Just when she was about to give up hope having a family, out of nowhere, four guys claim to be her older half-brothers.